Eternal Fourth Protections, commonly known as Bkulians, is a high-level sealing spell that requires connection to the Spirit Circuits to complete. It seals everything in a complete sphere, even the soil beneath it.
In the past, Jibril fired a Heavenly Smite on the Elven capital, where a rite of protection deployed by 3000 elves had failed to block the attack. In light of this, Think Nirvalen composed a greater rite of sealing. Deployed under the protection of Old Deus Kainas, the spell is strong enough to block a Heavenly Smite (but not against a Godly Smite).
It is stated in Volume 6, during the Great War, that the Eternal Fourth Protection was a spell developed by Think Nirvalen after it's knowledge was lost to the Flügel.